Definition
A conceptual relationship used in airplane energy management which states that the airplane's total energy at any moment equals the energy added by the engine (thrust) minus the energy lost to drag, with the difference distributed between kinetic energy (airspeed) and potential energy (altitude). It expresses the idea that thrust supplies energy, drag removes it, and pitch determines whether the remaining energy is held as speed or as height.
Plain English
It's the simple idea that an airplane's energy comes in from the engine, leaks out through drag, and whatever is left shows up as either speed or altitude. Pitch decides how that leftover energy is split between the two.
Context Anchor
Seen in energy management discussions, especially when learning how pitch and power affect climb, descent, acceleration, and deceleration.
Derivation
"Balance" comes from the Latin bilanx, meaning "having two scales." The term pictures energy on a set of scales: what the engine adds on one side, what drag takes away on the other, with airspeed and altitude sharing whatever is left.
Why Pilots Care
Understanding the equation lets a pilot trade altitude for speed or use excess power to gain both without creating stalls, overspeeds, or inefficient flight paths.
Analogy
Think of altitude and speed like two accounts that can trade value with each other. In a descent, the airplane can spend altitude to gain speed; in a climb, it may spend speed unless power adds more energy.
Grounding Statement
If you pull up without adding power, the airplane may climb briefly, but some of that climb comes from giving up airspeed.
Intuition Check
Do not read equation as something the pilot must calculate in the cockpit. Here it means a practical relationship: altitude, airspeed, and power must stay in balance.
Example Sentence 1
The instructor used the energy balance equation to explain why adding power without adjusting pitch caused the airplane to climb instead of accelerate.
Example Sentence 2
With excess thrust the energy balance equation showed that both altitude and airspeed could increase at the same time during the climb.